peertube-plugin-livechat/support/documentation/content/en/technical/slow_mode.md

title	description	weight	chapter	livechatnotranslation
MUC Slow mode	MUC Slow mode XEP	60	false	true

The livechat plugin includes a "slow mode" feature, to rate limit the number of messages that a user can send to a given MUC room. At time of writing, there were no XEP to describe such feature. Please find below a XEP draft, that will be submitted for review.

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XEP: MUC Slow Mode

Abstract: This specification describes a way to rate limit messages a single user can send to a MUC room, from the room configuration to the server and client handling of such a feature.

Author: John Livingston

1. Introduction

There are some contexts in which you want to be able to rate limit MUC messages. This could have multiple motivations: avoid flooding, garantee a better readability of the room when there are hundreds of active users, ...

This specification will propose to add an option to MUC rooms, allowing room owners to fix a time that users MUST wait between two messages. We will also specify how the server MUST reject messages send too quickly, and how clients SHOULD handle this feature (by preventing users to send messages without waiting the delay to be over).

2. Terminology

Bare JID: The user@host by which a user is identified outside the context of any existing session or resource; contrast with Full JID and Occupant JID.

Clients: the client software used by end-users to join MUC rooms.

Full JID: The <user@host/resource> by which an online user is identified outside the context of a room; contrast with Bare JID and Occupant JID.

Moderator: A room role that is usually associated with room admins but that can be granted to non-admins. Is allowed to edit room information. A moderator has a role of "moderator".

MUC: The multi-user chat protocol for text-based conferencing.

Occupant JID: The <room@service/nick> by which an occupant is identified within the context of a room; contrast with Bare JID and Full JID.

Role: A temporary position or privilege level within a room, distinct from a user's long-lived affiliation with the room; the possible roles are "moderator", "participant", and "visitor" (it is also possible to have no defined role). A role lasts only for the duration of an occupant's visit to a room.

Room JID: The room@service address of a room.

Room owner: users that have special access to a room, and that can edit room configuration. See XEP-0045 - Owner Use Cases.

Service Discovery Extensions: XEP-0128: Service Discovery Extensions.

Slow Mode: feature allowing to rate limit user messages in a MUC room.

Slow Mode duration: when the Slow Mode feature is active, specifies the time, in seconds, users must wait between two text messages.

3. Requirements

This document addresses the following requirements:

• Enable and configure the feature by editing the MUC room discovery information.
• How the server MUST reject messages that does not respect the parameters.
• How clients SHOULD handle rooms with such feature enabled.

4. MUC configuration

4.1 Activating Slow Mode in the MUC Room configuration

Your implementation CAN allow the Slow Mode feature to be set room by room, by its owners.

If room owners can configure the Slow Mode feature, the server MUST add a muc#roomconfig_slow_mode_duration field in the room configuration form.

This field MUST have its type equal to text-single.

This field SHOULD use Data Forms Validation, having its datatype equal to xs:integer.

The value of the field MUST be a positive integer. Any invalid value MUST be considered as equal to 0.

0 value means that the slow mode is disabled for this room. Any positive value is the time, in seconds, users must wait between two messages.

Here is an example of response the server could send when a client is querying room configuration form:

<iq from='coven@chat.shakespeare.lit'
    id='config1'
    to='crone1@shakespeare.lit/desktop'
    type='result'>
  <query xmlns='http://jabber.org/protocol/muc#owner'>
    <x xmlns='jabber:x:data' type='form'>
      <title>Configuration for "coven" Room</title>
      <instructions>
        Complete this form to modify the
        configuration of your room.
      </instructions>
      <field
          type='hidden'
          var='FORM_TYPE'>
        <value>http://jabber.org/protocol/muc#roomconfig</value>
      </field>
      <field
        var='muc#roomconfig_slow_mode_duration'
        type='text-single'
        label='Slow Mode (0=disabled, any positive integer= users can send a message every X seconds.)'
      >
        <validate xmlns='http://jabber.org/protocol/xdata-validate' datatype='xs:integer'/>
        <value>20</value>
      </field>
      <!-- and any other field... -->
    </x>
  </query>
</iq>

If the configuration is changed, the server SHOULD send a status code 104, as specified in XEP-0045 - Notification of configuration changes.

4.2 Client discovering

The feature can be enabled on a room:

• by the room owner, if your implementation allow them to set this option
• by a server-wide parameter

In other words: you can enable this feature, without adding the field in the room configuration form. This allows for example server admins to apply a rate limit server-wide, or to set the slow mode programmatically on any wanted criteria (number of users in the room, current server load, room context, ...).

In any case, to allow clients to discover that the feature is active, the server MUST respond on room information queries by adding a muc#roominfo_slow_mode_duration field. This field type MUST be text-single, and its value MUST be a positive integer.

0 value means that the slow mode is disabled for this room. Any positive value is the time, in seconds, users must wait between two messages.

Here is an example of response the server could send when a client is querying room information:

<iq from='coven@chat.shakespeare.lit'
    id='ik3vs715'
    to='hag66@shakespeare.lit/pda'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    <identity
        category='conference'
        name='The place to be'
        type='text'/>
    <feature var='http://jabber.org/protocol/muc'/>
    <x xmlns='jabber:x:data' type='result'>
      <field var='FORM_TYPE' type='hidden'>
        <value>http://jabber.org/protocol/muc#roominfo</value>
      </field>
      <field var='muc#roominfo_slow_mode_duration' type='text-single'>
        <value>2</value>
      </field>

      <!-- and any other field... -->
    </x>
  </query>
</iq>

If the slow mode duration is changed, the server SHOULD send a status code 104, as specified in XEP-0045 - Notification of configuration changes.

5. Server-side rate limiting

When the Slow Mode is enabled, server MUST NOT accept two consecutive messages from the same user, to the same room. Only messages containing at least one body tag must be taking into account (to avoid counting chatstate messages for example).

If a user bypass the limit, the server MUST reply an error stanza, that respects RFC 6120, especially:

• error_type MUST be wait, as described in RFC 6120 - Stanzas error - Syntax,
• error_condition MUST be policy-violation, as described in RFC 6120 - Stanzas error - Defined Stream Error Conditions,
• the stanza SHOULD contain a text tag explaining why the message was rejected, and this message SHOULD mention the slow mode duration so that user can understand why they can't post their message.

Here is an example or error stanza:

<message
  xmlns="jabber:client"
  type="error"
  to="crone1@shakespeare.lit/desktop" id="528df978-aa6b-422a-b987-056a810c4733" from="coven@chat.shakespeare.lit"
>
  <error type="wait">
    <policy-violation xmlns="urn:ietf:params:xml:ns:xmpp-stanzas" />
    <text xmlns="urn:ietf:params:xml:ns:xmpp-stanzas">
      You have exceeded the limit imposed by the slow mode in this room. You have to wait 2 seconds between messages. Please try again later
    </text>
  </error>
</message>

6. Client handling

When a user joins a room, the client SHOULD request room information as described in section "4.2 Client discovering", and look for the muc#roominfo_slow_mode_duration field.

If this field is present, and contains a valid strictly positive integer value, the client SHOULD display an information somewhere, to tell users that there is a slow mode limitation that applies to this room.

Moreover, each time a user sends a text message, the client SHOULD prevent the user to send another message before the timeout is passed. This COULD be done either by disabling the input field, or the submit button.

To avoid some frustrating behaviour, in case there is some lag on the server for example, the client SHOULD prevent sending new messages for a slightly longer duration, than the slow mode duration (for example by adding 100 or 200ms). Indeed, if the first message is processed with some delay by the server, it could consider that the duration is not passed yet when receiving the next one.